John Gruber has found out that cross-compilers are no longer allowed in iPhone OS 4.0. "My reading of this new language is that cross-compilers, such as the Flash-to-iPhone compiler in Adobe's upcoming Flash Professional CS5 release, are prohibited. This also bans apps compiled using MonoTouch - a tool that compiles C# and .NET apps to the iPhone. It's unclear what this means for tools like Titanium and PhoneGap, which let developers write JavaScript code that runs in WebKit inside a native iPhone app wrapper. They might be OK."

Baring in mind that the ObjectiveC runtime is fully accessible in C, and C is a language that Apple would seem to accept - the compiler simply needs to output plain C.

No.

Here's the clause from the agreement:

3.3.1 Applications may only use Documented APIs in the manner prescribed by Apple and must not use or call any private APIs. Applications must be originally written in Objective-C, C, C++, or JavaScript as executed by the iPhone OS WebKit engine, and only code written in C, C++, and Objective-C may compile and directly link against the Documented APIs (e.g., Applications that link to Documented APIs through an intermediary translation or compatibility layer or tool are prohibited).

Note the highlighted section. The INTENT of the clause is that code be written in C/Obj-C/C++/JS. Not cross-compiled INTO C and then compiled down in to the runtime.

That's pretty clear from this.

If you're not writing C/Obj-C/C++/JS for your code, technically you're in violation. In fact, arguable Googles Web Toolkit will violate this contract, since that code is originally in Java and compiled down in to JS.